Nucleic acids the term

The reference standards are used to quantitate the standards that are employed in the kits to generate the standard curves. The kit standards are recombinant single-stranded DNA molecules that are added to either negative serum or plasma at known concentrations. Because the standard curve is not constructed with reference standards, Chiron initially chose to use the term equivalent to describe the units of nucleic acid quantitation in clinical samples. An equivalent was defined as the amount of nucleic acid in a clinical sample that gave a signal equal to one molecule of the reference standard nucleic acid. The term copy rather than equivalent is used to describe the units of nucleic acid quantitation in the HIV-1 bDNA assay. The terms are now used interchangeably. 

In the 1940s and 1950s the pioneering studies of James and Elizabeth Miller provided early evidence for in vivo conversion of chemical carcinogens to reactive metabolites. They found that reactive metabolites of the aminoazo dye A, /V-dimcthyl-4-aminoazobenzene (DAB), a hepatocarcinogen in rats, would bind covalently to proteins and nucleic acids. The term, metabolic activation, was coined by the Millers to describe this process. Moreover they demonstrated that covalent binding of these chemicals was an essential part of the carcinogenic process. 

The term nucleoside was once restricted to pyrimidine and purine A-glycosides of D-ribofuranose and 2-deoxy-D-ribofuranose, because these are the substances present in nucleic acids. The term is used more liberally now with respect to the carbohydrate portion, but is still usually limited to pyrimidine and purine substituents at the anomeric carbon. Uridine is a representative pyrimidine nucleoside it bears a D-ribofuranose group at N-1. Adenosine is a representative purine nucleoside its carbohydrate unit is attached at N-9. 

The terms nucleoside and nucleotide in the strictest sense refer to N- lycosides and phosphorylated N-glycosides, respectively, derived from nucleic acids. The term is now used, however, in several broader ways. Thus, adenosine triphosphate (ATP) is not derived from nucleic acids, but is quite legitimately a nucleotide through its relation to adenosine monophosphate (AMP), which is so derived. Other N-ribosides, such as nicotinamide mononucleotide (NMN), are called nucleotides only by extension and anal-... 

Both pynmidme and purine are planar You will see how important this flat shape is when we consider the structure of nucleic acids In terms of their chemistry pyrimidine and purine resemble pyndme They are weak bases and relatively unreactive toward elec trophilic aromatic substitution... 

Probes that mediate capture of the target nucleic acid are termed capture extenders. These probes are approximately 50 bases, one portion (20 to 40 bases) of which is complementary to the target, while the second portion (approximately 20 bases) binds the probe-target complex to a capture probe that is coupled to the surface of a microtiter plate well. 

The bases are either monocyclic pyrimidines or bicyclic purines (see Section 14.1). Three pyrimidine bases are encountered in DNA and RNA, cytosine (C), thymine (T) and uracil (U). Cytosine is common to both DNA and RNA, but uracil is found only in RNA and thymine is found only in DNA. In the nucleic acid, the bases are linked through an A-glycoside bond to a sugar, either ribose or deoxyribose the combination base plus sugar is termed a nucleoside. The nitrogen bonded to the sugar is that shown. 

Splicing occurs in a large protein-nucleic acid complex, termed the spUceosome. Components of the spliceosome are, apart from the pre-mRNA, a number of proteins and small RNAs, termed the Ul, U2, U4, U5 and U6. The RNAs found in the spUceo-some are bound to specific proteins. The complexes are termed snRNPs (small nuclear ribonucleoprotein). Depending upon the type of RNA bound, there are Ul, U2, U5 and U4/U6 snRNPs. 

The term nucleoside was originally proposed by Levene and Jacobs in 1909 for the carbohydrate derivatives of purines (and, later, of pyrimidines) isolated from the alkaline hydrolyzates of yeast nucleic acid. The phosphate esters of nucleosides are the nucleotides, which, in polymerized forms, constitute the nucleic acids of all cells.2 The sugar moieties of nucleosides derived from the nucleic acids have been shown, thus far, to be either D-ribose or 2-deoxy-D-eri/fAro-pentose ( 2-deoxy-D-ribose ). The ribo-nucleosides are constituents of ribonucleic acids, which occur mainly in the cell cytoplasm whereas 2-deoxyribo -nucleosides are components of deoxypentonucleic acids, which are localized in the cell nucleus.3 The nucleic acids are not limited (in occurrence) to cellular components. They have also been found to be important constituents of plant and animal viruses. 

The term "nucleoside refers to the A -glycosylpurines and jV-glycosylpyrimidines derived from nucleic acids. The common chemical feature of purine nucleosides is a -D-ribofuranosyl or a 2 -deoxy- 8-D-ribofuranosyl moiety linked to N9 of the purine base. Adenosine (1) and guanosine (2) are the most common purine nucleosides of RNA, whereas DNA contains 2 -de-oxyadenosine (3) and 2 -deoxyguanosine (4). 

Nucleotides have compact shapes with several interactions between non-bonded atoms, and their molecular geometry is well reflected in the helical structure of nucleic acids. The shapes of nucleotides can be described in terms of four parameters, namely ... 

The term nucleotide was introduced in 1908 by Levene to refer to phosphate esters of nucleosides, which were so named because they contained a sugar in glycostdfc linkage with the purine and pyrimidine bases of the nucleic acids. The latter term, of course, represents the source from which the bases were first isolated, the nuclei of animal cells. 

The nucleic acids were discovered by Miescher in 1868-1869, when he isolated from pus cell nuclei a material which contained phosphorus, was soluble in alkali, but precipitated under acidic conditions. This material was subsequently prepared from other sources and when freed from protein it was called nucleic acid, a term introduced by Altman in 1889. The classical preparations of nucleic acid from yeast yielded a product which we now recognize as ribonucleic acid (RNA). The nucleic acid prepared from thymus glands, thymonucleic acid, was also extensively studied this material [which, in present terms, was deoxyribonucleic acid (DNA)) was different from yeast nucleic acid. From hydrolysates of these preparations the heterocyclic bases were isolated and characterized. At one time, yeast and thymus nucleic acids were thought to be representative of plant and animal nucleic acids, respectively (3). By 1909, it was apparent that yeast nucleic acid contained adenine, guanine, cytosine, uracil, phosphoric acid, and a sugar which Levene showed at that time to be D-ribose. Thymonucleic acid yielded adenine, guanine, cytosine, thymine, phosphoric acid, and a sugar which was not identified correctly until 1929, when it was characterized as 2-deoxy-D-ribose. 

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